Realistic simulation of Io's Pele plume and its effects on Io's atmosphere

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Abstract

The direct simulation Monte Carlo (DSMC) method is used to investigate gas and dust in Io's giant Pele plume as well as the interaction of giant plumes with other plumes, with Jupiter's plasma torus, and with Io's sublimation atmosphere. Three-dimensional simulations of time-varying systems are performed on up to 2002 processors. Methods for the efficient simulation of interactions between neutral gas and dust particles and between neutral gas and ions (including chemistry) are developed. Simulations are load-balanced dynamically and the grid structure adapts to resolve (potentially moving) regions of high density. Three-dimensional simulations of the Pele plume show how gas erupting from cracks and holes in a lava lake produces the observed plume and deposition pattern. Small-scale features of the lava lake are found to explain the asymmetric shape of the giant deposition ring. Dust particles are included in the simulations and the computed deposition patterns of different sizes of dust are compared with observations in order to obtain a best-fit size distribution for particles in the plume. The interaction of Pele and Pillan is investigated by the simultaneous simulation of both plumes. Giant plumes on Io's equator and north pole are simulated alongside ions which move with Jupiter's magnetic field, and a chemistry model allows for high-energy collisions to produce daughter species. The effect of plasma bombardment on plumes is found to depend on the location of the plumes, and it gives rise to a large, diffuse cloud of neutrals surrounding the plumes. The dense gas in plume canopies also influences the trajectories of ions in the plasma torus, causing ion slip and further asymmetry in the plumes. Dynamic simulations of plumes on Io's equator and at 30 degrees north latitude over an Io day show how plumes interact with Io's sublimation atmosphere. Plume material becomes suspended in the atmosphere, displacing many times the night-side mass of the plume in sublimated material. The total mass of the atmosphere, however, increases by only a fraction of the plume's night-side mass as the surface frost effectively maintains vapor pressure equilibrium.